Balance shaft having reduced mass and inertia

ABSTRACT

A balance weight having one or more journals with a reduced mass portion disposed between a pair of journal portions that define circumferentially extending bearing surfaces. The reduced mass portion has a body, which defines a circumferentially extending bearing surface that is concentric with the bearing surfaces on the journal portions, and at least one stiffening structure that is configured to resist flexing of the journal portions relative to one another due to the transmission of bending loads through the balance shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/984,762 filed May 21, 2018 and claims the benefit of U.S. ProvisionalPatent Application No. 62/531,671 filed Jul. 12, 2017. The disclosure ofeach of the above-referenced applications is incorporated by referenceas if fully set forth in detail herein.

FIELD

The present disclosure relates to a balance shaft having reduced massand inertia.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Balance shafts are commonly employed to counteract vibrations ininternal combustion engines that are not inherently balanced. A typicalbalance shaft can include one or more journals, which establish therotational axis of the balance shaft, and one or more counterweightsthat can each be sized, shaped and positioned relative to the rotationalaxis so as to place mass at a predetermined offset from the rotationalaxis.

While the known balance shaft configurations are suited for theirintended purpose, it is desirable that the overall mass and inertia ofthe balance shaft be minimized. Accordingly, there is a need in the artfor a reduced mass balance shaft with increased stiffness.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In one form, the present teachings provide a balance shaft having firstand second journals and at least one counterweight. The first and secondjournals define a rotational axis. The at least one counterweight isfixedly coupled to the first and second journals. The first journaldefines a first journal portion, a second journal portion and a reducedmass portion that is disposed along the rotational axis between thefirst and second journal portions. The first journal portion defines afirst circumferentially extending bearing surface and the second journalportion defines a second circumferentially extending bearing surface.The reduced mass portion is disposed axially between the first andsecond circumferentially extending bearing surfaces and includes a bodyand a stiffening structure. The body is fixedly coupled to the first andsecond journal portions and defines a third circumferentially extendingbearing surface that is concentric with the first and secondcircumferentially extending bearing surfaces. The stiffening structureintersects the body and the first and second journal portions andterminates radially inwardly of the first circumferentially extendingbearing surface such that a void space is disposed between the first andsecond journal portions at a location that is radially outwardly of thestiffening structure. The stiffening structure defines a first pocket,which is disposed adjacent the first journal portion and a secondpocket, which is disposed adjacent the second journal portion. The firstand second pockets are spaced apart from one another along therotational axis to form a land there between.

In another form, the present teachings provide balance shaft havingfirst and second journals and at least one counterweight. The first andsecond journals define a rotational axis. The at least one counterweightis fixedly coupled to the first and second journals. The first journaldefines a first journal portion, a second journal portion and a reducedmass portion that is disposed along the rotational axis between thefirst and second journal portions. The first journal portion defines afirst circumferentially extending bearing surface and the second journalportion defines a second circumferentially extending bearing surface.The reduced mass portion is disposed axially between the first andsecond circumferentially extending bearing surfaces and includes a bodyand at least one stiffening structure. The body is fixedly coupled tothe first and second journal portions and at least partly defines athird circumferentially extending bearing surface that is concentricwith the first and second circumferentially extending bearing surfaces.The at least one stiffening structure is fixedly coupled to the firstand second journal portions and terminates radially inwardly of thefirst circumferentially extending bearing surface such that a void spaceis disposed between the first and second journal portions at a locationthat is radially outwardly of the stiffening structure. In across-section of the balance shaft taken perpendicular to the rotationalaxis, the void space extends between the rotational axis and the body.

In another form, the present disclosure provides a balance shaft havingfirst and second journals, which define a rotational axis, and at leastone counterweight that is fixedly coupled to the first and secondjournals. The first journal defines a first journal portion, a secondjournal portion and a reduced mass portion that is disposed along therotational axis between the first and second journal portions. The firstjournal portion defines a first circumferentially extending bearingsurface, while the second journal portion defines a secondcircumferentially extending bearing surface. The reduced mass portionhas a body and a stiffening structure. The body is fixed to and spansbetween the first and second journal portions. The body is shaped as acylindrical segment having a third circumferentially extending bearingsurface and an inboard surface. The inboard surface is offset from therotational axis and intersects the third circumferentially extendingbearing surface. The stiffening structure is fixed to and spans betweenthe first and second journal portions. The stiffening structure isdisposed radially inside of a cylindrically-shaped perimeter defined bythe first, second and third circumferentially extending bearingsurfaces. The stiffening structure is offset from the rotational axissuch that the rotational axis is disposed between the body and thestiffening structure so that a void space is formed laterally throughthe first journal. The void space is bounded on four sides by an inboardsurface of the stiffening structure, the inboard surface of the body, aninterior surface of the first journal portion and an interior surface ofthe second journal portion.

In yet another form, the present disclosure provides a a balance shafthaving first and second journals, which define a rotational axis, and atleast one counterweight that is fixedly coupled to the first and secondjournals. The first journal defines a first journal portion, a secondjournal portion and a reduced mass portion that is disposed along therotational axis between the first and second journal portions. The firstjournal portion defines a first circumferentially extending bearingsurface, while the second journal portion defines a secondcircumferentially extending bearing surface. The reduced mass portionhas a body that is fixed to and spans between the first and secondjournal portions. The body has a third circumferentially extendingbearing surface and an inboard surface. The first journal has acylindrically-shaped perimeter that is defined by the first, second andthird circumferentially extending bearing surfaces. The inboard surfaceof the body is disposed between the rotational axis and the thirdcircumferentially extending bearing surface. At least a portion of theinboard surface of the body is concave in shape in a plane that isperpendicular to the rotational axis.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a perspective view of a first balance shaft constructed inaccordance with the teachings of the present disclosure;

FIG. 2 is a side elevation view of the balance shaft of FIG. 1;

FIG. 3 is a section view taken along the line 3-3 of FIG. 2;

FIG. 4 is top plan view of a portion of the balance shaft of FIG. 1;

FIG. 5 is a section view taken along the line 5-5 of FIG. 4;

FIG. 6 is a section view taken along the line 6-6 of FIG. 2;

FIG. 7 is a perspective view of a second balance shaft constructed inaccordance with the teachings of the present disclosure;

FIG. 8 is a side elevation view of the balance shaft of FIG. 7;

FIG. 9 is a section view taken along the line 9-9 of FIG. 8;

FIG. 10 is top plan view of a portion of the balance shaft of FIG. 7;

FIG. 11 is a section view taken along the line 11-11 of FIG. 10;

FIG. 12 is a perspective view of a third balance shaft constructed inaccordance with the teachings of the present disclosure;

FIG. 13 is a side elevation view of the balance shaft of FIG. 12;

FIG. 14 is a section view taken along the line 14-14 of FIG. 13;

FIG. 15 is top plan view of a portion of the balance shaft of FIG. 12;and

FIG. 16 is a section view taken along the line 16-16 of FIG. 15.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2 of the drawings, a first balance shaftconstructed in accordance with the teachings of the present disclosureis generally indicated by reference numeral 10. The balance shaft 10 caninclude first and second journals 12 and 14 and at least onecounterweight 16. The first and second journals 12 and 14 can cooperateto define a rotational axis 18 about which the balance shaft 10 isintended to rotate. With additional reference to FIG. 6, the at leastone counterweight 16 can be conventional in its construction. In theexample provided, the balance shaft 10 is a “linear” balance shaft andas such, the at least one counterweight 16 is fixedly coupled to thefirst and second journals 12 and 14 and is sized and positioned tooffset a center of gravity CG of the balance shaft 10 from therotational axis 18. It will be understood, however, that the balanceshaft 10 could be configured as a “couple type” balance shaft in whichcase the counterweights 16 would be fixedly coupled to the first andsecond journals 12 and 14 in a manner that does not offset the center ofgravity of the balance shaft from the rotational axis 18. The balanceshaft 10 can be unitarily and integrally formed in one or more desiredoperations, such as machining, casting or forging, but it will beappreciated that the balance shaft 10 could be formed as an assembly(e.g., with the counterweight(s) 16 being assembled to a remainingportion of the balance shaft 10).

The first and second journals 12 and 14 can be formed differently fromone another, but in the example provided, the first and second journals12 and 14 are identical in their construction. As such, only adiscussion of the first journal 12 will be provided herein.

With reference to FIGS. 2 through 5, the first journal 12 can define afirst journal portion 30, a second journal portion 32 and a reduced massportion 34 that is disposed along the rotational axis 18 between thefirst and second journal portions 30 and 32. The first journal portion30 can define a first circumferentially extending bearing surface 36 andthe second journal portion 32 can define a second circumferentiallyextending bearing surface 38. In the particular example provided, boththe first and second circumferentially extending bearing surfaces 36 and38 extend fully about the rotational axis 18, but it will be appreciatedthat one or both of the first and second circumferentially extendingbearing surfaces 36 and 38 can extend only partly about the rotationalaxis 18.

The reduced mass portion 34 can be disposed axially between the firstand second circumferentially extending bearing surfaces 36 and 38 andcan include a body 40 and a stiffening structure 42. The body 40 can befixedly coupled to (e.g., intersect) the first and second journalportions 30 and 32 and can define a third circumferentially extendingbearing surface 44 that is concentric (e.g., coincide or co-extend) withthe first and second circumferentially extending bearing surfaces 36 and38. The stiffening structure 42 can intersect the body 40 and the firstand second journal portions 30 and 32 and can terminate radiallyinwardly of the first circumferentially extending bearing surface 36such that a void space 48 is disposed between the first and secondjournal portions 30 and 32 at a location that is radially outwardly ofthe stiffening structure 42.

The stiffening structure 42 is configured to stiffen the first journal12 to resist flexing of the first journal portion 30 relative to thesecond journal portion 32 due to the transmission of bending loadsthrough the balance shaft 10. The stiffening structure 42 can define afirst pocket 52, which is disposed adjacent the first journal portion30, and a second pocket 54 that is disposed adjacent the second journalportion 32. The first and second pockets 52 and 54 can be spaced apartfrom one another along the rotational axis 18 to form a land 56 therebetween.

The first and second pockets 52 and 54 can be formed in any desiredmanner and need not be configured in an identical manner. For example,at least one of the first and second pockets 52 and 54 can be shaped asa portion of a prism, such as a triangular prism. In the exampleprovided, the first pocket 52 is formed as a right triangular prism, thefirst pocket 52 is oriented so that a surface 60 of the first pocket 52is disposed proximate the first journal portion 30 and a vertex 62 ofthe first pocket 52 is disposed proximate the land 56, and the secondpocket 54 is configured as a mirror image of the first pocket 52 (i.e.,the first pocket 52 is mirrored about a plane that is perpendicular tothe rotational axis 18 and which bisects the land 56 to form the secondpocket 54). Alternatively, one or both of the first and second pockets52 and 54 could be formed as a portion of a pyramid, cone, cylinder orpolyhedron (e.g., a complex polyhedron, such as a regular polyhedron).Also alternatively, at least one of the first and second pockets 52 and54 could be formed with at least one curved surface (not shown). The atleast one curved surface could be shaped such that a conic section isformed by the intersection of the at least one curved surface and aplane that is taken through the stiffening structure 42.

In the example provided, a width of the land 56 as measured in adirection parallel to the rotational axis 18 can be larger than a widthof the first pocket 52 as measured in the direction parallel to therotational axis 18. It will be appreciated, however, that width of theland 56 could be smaller than the width of one or both of the first andsecond pockets 52 and 54.

Optionally, a pair of circumferentially extending notches 70 can beformed in the reduced mass portion 34 to further reduce the mass of thefirst journal 12 and aid in placing the center of gravity CG of thebalance shaft 10 in a desired location. The circumferentially extendingnotches 70 can intersect the third circumferentially extending bearingsurface 44 such that the third circumferentially extending bearingsurface 44 extends between the circumferentially extending notches 70through a predetermined angle 72. The predetermined angle 72 can begreater than or equal to sixty degrees, and is more preferably greaterthan or equal to ninety degrees. The predetermined angle 72 can beoriented such that it is bisected by a first plane 78 that isperpendicular to the rotational axis 18, is intersected at a singlepoint by the rotational axis 18 and optionally includes the center ofgravity CG of the balance shaft 10. The circumferentially extendingnotches 70 can be formed in any desired manner. In the example provided,the circumferentially extending notches 70 are generally V-shaped havinga vertex 82 that is disposed in a second plane 80 that is perpendicularto the first plane 78. Optionally, one or more passageways may be formedthrough stiffening structures 42 in order to allow lubricant to escapethe pockets 52 and/or 54, thus preventing buildup and unintendedimbalance.

It will be appreciated that references to a “plane” made herein refer toa plane that exists in a two-dimensional space (i.e., a Euclidianplane).

With reference to FIGS. 7 through 11, a second balance shaft constructedin accordance with the teachings of the present disclosure is generallyindicated by reference numeral 10 a. The balance shaft 10 a is generallysimilar to the balance shaft 10 of FIG. 1, except for the configurationof the first and second journals 12 a and 14 a. As the second journal 14a is identical to the first journal 12 a in this example, only adiscussion of the first journal 12 a will be provided herein.

The first journal 12 a can define a first journal portion 30, a secondjournal portion 32 and a reduced mass portion 34 a that can be disposedalong the rotational axis 18 between the first and second journalportions 30 and 32. The first journal portion 30 defines a firstcircumferentially extending bearing surface 36, while the second journalportion 32 defines a second circumferentially extending bearing surface38.

The reduced mass portion 34 a can be disposed axially between the firstand second circumferentially extending bearing surfaces 36 and 38 andcan include a body 40 a and at least one stiffening structure 42 a. Thebody 40 a can be fixedly coupled to the first and second journalportions 30 and 32 and can at least partly define a thirdcircumferentially extending bearing surface 44 a that is concentric withthe first and second circumferentially extending bearing surfaces 36 and38. The at least one stiffening structure 42 a can be fixedly coupled tothe first and second journal portions 30 and 32 and can terminateradially inwardly of the first circumferentially extending bearingsurface 36 such that a void space 48 a is disposed between the first andsecond journal portions 30 and 32 at a location that is radiallyoutwardly of the at least one stiffening structure 42 a. In across-section of the balance shaft 10 a taken perpendicular to therotational axis 18, the void space 48 a extends between the rotationalaxis 18 and the body 40 a.

In the particular example provided, two stiffening structures 42 a areprovided that intersect opposite circumferential ends of the body 40 a.In this example, a portion of the third circumferentially extendingbearing surface 44 a is formed on each of the stiffening structures 42a. Optionally, one or more passageways may be formed through stiffeningstructures 42 a in order to allow lubricant to escape the void space 48a, thus preventing buildup and unintended imbalance. It is furtheroptionally contemplated that the stiffening structures 42 and 42 a maybe superimposed, which would increase the number of pockets and/or couldincrease the stiffness of the reduced mass portion.

With reference to FIGS. 12 through 16, a third balance shaft constructedin accordance with the teachings of the present disclosure is generallyindicated by reference numeral 10 b. The balance shaft 10 b is generallysimilar to the balance shaft 10 a of FIG. 7, except for theconfiguration of the first and second journals 12 b and 14 b. As thesecond journal 14 b is identical to the first journal 12 b in thisexample, only a discussion of the first journal 12 b will be providedherein.

The first journal 12 b can define a first journal portion 30, a secondjournal portion 32 and a reduced mass portion 34 b that can be disposedalong the rotational axis 18 between the first and second journalportions 30 and 32. The first journal portion 30 defines a firstcircumferentially extending bearing surface 36, while the second journalportion 32 defines a second circumferentially extending bearing surface38.

The reduced mass portion 34 b can be disposed axially between the firstand second circumferentially extending bearing surfaces 36 and 38 andcan include a body 40 b and at least one stiffening structure 42 b. Thebody 40 b can be fixedly coupled to the first and second journalportions 30 and 32 and defines a third circumferentially extendingbearing surface 44 b that is concentric with the first and secondcircumferentially extending bearing surfaces 36 and 38. The at least onestiffening structure 42 b can be fixedly coupled to the first and secondjournal portions 30 and 32 and can terminate radially inwardly of thefirst circumferentially extending bearing surface 36 such that a voidspace 48 b is disposed between the first and second journal portions 30and 32 at a location that is radially outwardly of the at least onestiffening structure 42 b. In a cross-section of the balance shaft 10 ataken perpendicular to the rotational axis 18, the void space 48 bextends between the rotational axis 18 and the body 40 b. The void space48 b can optionally extend about the at least one stiffening structure42 b and between the rotational axis 18 and the body 40 b to form awindow W that is disposed through the first journal 12 b.

The rotational axis 18 can extend longitudinally between the body 40 band the at least one stiffening structure 42 b. The at least onestiffening structure 42 b can comprise a beam having a first surface 100and a second surface 102 that is spaced more distantly from therotational axis 18 than the first surface 100. In the example provided,the first and second surfaces 100 and 102 are parallel to one another,but it will be appreciated that the second surface 102 could be shapeddifferently. One benefit of the embodiment shown in FIGS. 12-16 is thatit allows lubricant to readily drain from between the body 40 b and thestiffening structure 42 b.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A balance shaft having first and second journals and at least one counterweight, the first and second journals defining a rotational axis, the at least one counterweight being fixedly coupled to the first and second journals; wherein the first journal defines a first journal portion, a second journal portion and a reduced mass portion disposed along the rotational axis between the first and second journal portions, the first journal portion defining a first circumferentially extending bearing surface, the second journal portion defining a second circumferentially extending bearing surface, the reduced mass portion having a body and a stiffening structure, the body being fixed to and spanning between the first and second journal portions, the body being shaped as a cylindrical segment having a third circumferentially extending bearing surface and an first medial surface, the first medial surface being offset from the rotational axis and intersecting the third circumferentially extending bearing surface, the stiffening structure being fixed to and spanning between the first and second journal portions, the stiffening structure being disposed radially inside of a cylindrically-shaped perimeter defined by the first, second and third circumferentially extending bearing surfaces, the stiffening structure having a second medial surface that is offset from the rotational axis such that the rotational axis is disposed between the body and the stiffening structure so that a void space is formed laterally through the first journal, the void space being bounded on four sides by the second medial surface of the stiffening structure, the first medial surface of the body, an interior surface of the first journal portion and an interior surface of the second journal portion.
 2. The balance shaft of claim 1, wherein the first circumferentially extending bearing surface extends fully about the rotational axis.
 3. The balance shaft of claim 2, wherein the second circumferentially extending bearing surface extends fully about the rotational axis.
 4. The balance shaft of claim 1, wherein a portion of the first medial surface of the body and a portion of the second medial surface of the stiffening structure are parallel to one another.
 5. The balance shaft of claim 4, wherein a portion of an outboard surface of the stiffening structure is parallel to the portion of the first medial surface of the body.
 6. The balance shaft of claim 1, wherein the rotational axis and the center of gravity of the balance shaft are disposed in a plane, and wherein the plane is perpendicular to the first medial surface of the body, the inboard surface of the stiffening structure.
 7. The balance shaft of claim 1, wherein the rotational axis and the center of gravity of the balance shaft are disposed in a plane, and wherein the interior surfaces of the first and second journal portions are perpendicular to the plane.
 8. A balance shaft having first and second journals and at least one counterweight, the first and second journals defining a rotational axis, the at least one counterweight being fixedly coupled to the first and second journals; wherein the first journal defines a first journal portion, a second journal portion and a reduced mass portion disposed along the rotational axis between the first and second journal portions, the first journal portion defining a first circumferentially extending bearing surface, the second journal portion defining a second circumferentially extending bearing surface, the reduced mass portion having a body that is fixed to and spans between the first and second journal portions, the body having a third circumferentially extending bearing surface and an a medial surface, wherein the first journal has a cylindrically-shaped perimeter that is defined by the first, second and third circumferentially extending bearing surfaces, wherein the medial surface of the body is disposed between the rotational axis and the third circumferentially extending bearing surface, and wherein at least a portion of the medial surface of the body is concave in shape in a plane that is perpendicular to the rotational axis.
 9. A balance shaft having first and second journals and at least one counterweight, the first and second journals defining a rotational axis, the at least one counterweight being fixedly coupled to the first and second journals; wherein the first journal defines a first journal portion, a second journal portion and a reduced mass portion disposed along the rotational axis between the first and second journal portions, the first journal portion defining a first circumferentially extending bearing surface, the second journal portion defining a second circumferentially extending bearing surface, the reduced mass portion being disposed axially along the rotational axis between the first and second circumferentially extending bearing surfaces and including a body and a stiffening structure, the body being fixedly coupled to the first and second journal portions and defining a third circumferentially extending bearing surface that is concentric with the first and second circumferentially extending bearing surfaces, the stiffening structure intersecting the body and the first and second journal portions and terminating radially inwardly of the first circumferentially extending bearing surface such that a void space is disposed between the first and second journal portions at a location that is radially outwardly of the stiffening structure; wherein the stiffening structure defines a first pocket, which is disposed adjacent the first journal portion, and a second pocket, which is disposed adjacent the second journal portion, and wherein the first and second pockets are spaced apart from one another along the rotational axis to form a land there between. 